<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html><head><style type="text/css"></style><title>Re: Soundboard crown</title></head><body> <div>Hi all,</div> <div>At 8:36 PM +0300 10/8/03, Calin Tantareanu wrote:</div> <blockquote type="cite" cite><br></blockquote> <blockquote type="cite" cite>I have followed the numeorus discussions on this list about rib-crowned vs.</blockquote> <blockquote type="cite" cite>compression crowned soundboards with great interest.<br> However, I am asking myself if a soundboard always needs  crown in order to<br> work properly?</blockquote> <div><br></div> <div>Probably not, but if you build a flat board and you dry the panel prior to gluing the ribs, you'll end up with compression crown by default, possibly the worst type of sound board you could construct.</div> <div><br></div> <blockquote type="cite" cite>I heard about some old pianos with no measurable crown that sound very good.</blockquote> <div><br></div> <div>Maybe, but they likely sounded better at some earlier time.</div> <div><br></div> <blockquote type="cite" cite>I read that harpsichords do not have crowned boards (except the</blockquote> <blockquote type="cite" cite>Italian ones).</blockquote> <div><br></div> <div>In general, harpsichords have thin board which are dried down before installation, the panel is glued in and encouraged to expand upwards as it takes up moisture.</div> <div><br></div> <blockquote type="cite" cite>So, why is a crown necessary?</blockquote> <div><br></div> <div>As Dale mentioned in his post<font color="#0000FF"> (hi Dale its good to read that you're back)</font>, a down bearing load on a flat panel will cause the panel to experience tension as it is forced down into a reverse crown. You can imagine how long it might take for the fist hint of summer to take out such a board. When considering a crowned panel, as the board sinks under the down bearing load at the time of set up, and over time as compression/tension set takes its toll, the sound board panel will tend to be further compressed as the crown recedes. This will tend to encourage an extension of the life of the panel rather than a shortening, as would be the case if the panel were to be manufactured as a flat panel.</div> <div><br></div> <blockquote type="cite" cite>Would a flat board, but with enough downbearing for the strings, work or</blockquote> <blockquote type="cite" cite>not?</blockquote> <div><br></div> <div>It would if it was designed appropriately, but why would you build a design which would fail earlier than an alternative? No serious piano manufacture should continue to build CC boards. They are doomed to premature failure, for numerous reasons which have been discussed at length on this list.</div> <div><br></div> <div>I am doing a lot of sound board research at present. This is why I haven't been posting to the list lately.</div> <div><br></div> <div>There was some list discussion about sound board presses recently. I got the first image of my vacuum sound board laminating press prepared for the web site yesterday. The image below shows the press, with a test strip of sound board panel and one rib being pressed.</div> <div><br></div> <div>http://overspianos.com.au/vacpress.jpg</div> <div><br></div> <div>I haven't written a text page for the image yet. The press is 6' x 8' (1800mm x 2400 mm). The vacuum pump is a Becker 3ph 2 hp unit.</div> <div><br></div> <div>A cutaway of the pump can be seen at;</div> <div><br></div> <div>http://www.becker-international.com/en_z010.html</div> <div><br></div> <div>It can pump 28 cfm when unrestricted and the vacuum can be adjusted from 1.5 psi to 12 psi. (12 psi will yield a hold-down pressure of around 0.75 tons/square foot - or 0.8 atmospheres). We use the minimum 1.5 psi vacuum for gluing the panel to the ribs. The vacuum diaphragm is a fibreglass reinforced vinyl, fitted to a lightweight RHS frame which can be lifted on and off the table with ease. The vacuum is delivered from the pump to the the table using the RHS frame as a vacuum plenum. A series of holes on the inner edge of the RHS allow the air to be evacuated from around the perimeter of the table. Apart from its use as a sound board assembly table, the press is also very useful for gluing veneer to panels. We will also use it for the manufacture of the laminated sound board panels which we are using for our own piano. By the way, the poser in the image is my Rottweiler 'Harry'. He likes to fossick around the workshop chewing the odd sound board off-cut.</div> <div><br></div> <div>Best,</div> <div>Ron O.</div> <x-sigsep><pre>-- </pre></x-sigsep> <div><font size="-2" color="#000000"><br> </font><font face="Times New Roman" size="+1" color="#0000FF"><b>OVERS PIANOS - SYDNEY</b></font></div> <div><font color="#000000"><i>    </i></font><font color="#0000FF"><i> Grand Piano Manufacturers</i></font><font color="#000000"><br>      _______________________</font></div> <div><font size="-2" color="#000000"><br></font></div> <div><font color="#000000">Web http://overspianos.com.au</font></div> <div><font color="#000000">mailto:ron@overspianos.com.au</font></div> <div><font color="#000000">     _______________________</font></div> </body> </html>